Display devices are widely used in many consumer and commercial applications. Display devices generally use light in order to display a visible image, especially in the dark. As is well known, display devices generally include active displays in which every picture element (pixel) emits light, and passive displays which use a source of light to project through the display panel. The source of light may be supplied by a backlight unit. Examples of active displays are cathode ray tubes (CRT) and light emitting diode (LED) displays. An example of a passive display is a liquid crystal display (LCD).
A backlight unit of an LCD will now be described. Backlight units generally include a light source such as a lamp, a reflecting sheet, a light guide panel and a diffusing sheet. The backlight unit and the display panel are generally enclosed within a mold frame and a top chassis.
FIGS. 1, 2, 3 and 4 illustrate a conventional backlight unit of an LCD. FIG. 1 is a top view of a conventional LCD module. Referring to FIG. 1, the image of the LCD is displayed on the area marked with dotted lines. This area is generally called the active area, and the outside of the active area is enclosed with a top chassis 8. It is generally desirable to reduce the distance A between the top chassis 8 and the active area, in order to provide compact LCDS.
FIG. 2 is a cross-sectional view illustrating a conventional LCD module. Referring to FIG. 2, a conventional LCD has a light guide panel 2 which guides light to a display panel. Two diffuser sheets 3 (or diffuser and prism sheets) are mounted over the light guide panel 2. A display panel including a thin film transistor (TFT) substrate 4 and a color filter substrate 5 is mounted over these diffuser sheets. The TFT substrate 4 is connected to a PCB (Printed Circuit Board) substrate 6 having TAB IC (Tape Automated Bonding Integrated Circuit) 7. The light guide panel 2, diffuser sheets 3, TFT substrate and PCB substrate are mounted in the grooves of a mold frame 1. The mold frame 1 is combined with the top chassis 8, thereby holding and protecting the display panel and the backlight unit. Since the module size becomes smaller as the distance A is reduced, the distance B between the mold frame 1 and the active area also is generally reduced.
FIG. 3 is a top view of the inside construction of a conventional backlight unit. Referring to FIG. 3, the mold frame 1 is grooved so that a light source 9, the guide panel 2 and the PCB substrate 6 may be mounted thereon. The light guide panel 2 is mounted in the middle of the mold frame 1 and the lamp 9 is horizontally mounted on one side of the mold frame 1. Generally, there is some space between the lamp 9 and the light guide panel 2 so that the light guide panel 2 can receive light from the lamp 9 and send light to the display panel. Therefore, it is possible to damage the lamp when the LCD module is shaken or external forces are imparted to the LCD module.
To solve this problem, the light guide panel 2 includes a light guide projection 10 and a side of the mold frame includes a groove 11. The light guide projection 10 of the light guide panel 2 can thus be fitted to the groove 11 so that the mold frame can fixedly hold the light guide panel 2.
FIG. 4 is an enlarged diagram illustrating light concentration in a portion D of FIG. 3. Referring to FIG. 4, light is concentrated in the right-angled corners 10a, 10b of the light guide projection 10. When light from the lamp reaches the boundary of the light guide projection, light is partially reflected and partially transmitted to the mold frame 1. When light reaches the mold frame 1, light is reflected and is sent back to the boundary of the light guide panel 2. Then, light is partially reflected to air C and partially transmitted to the inside of the light guide panel 2. Reflection and transmission of light are repeated in air C between the light guide panel 2 and the mold frame 1, so that light may be concentrated at the corners 10a, 10b of the light guide projection 10 of the light guide panel 2.
As a result of this concentration, the light guide projection 10 of the light guide panel 2 may be brighter compared to other portions. The concentrated light may result in a poor quality LCD. Moreover, as the distance A between the module and active area is reduced, the light concentration may increase.